1. Field of the Invention
This invention relates to a laser spot projector, and more particularly to a laser spot projector for use with a laser coagulation system in which a laser beam is radiated as a spot into a portion selected to be thermally coagulated.
2. Description of the Prior Art
There have long been known laser coagulation systems in which during an ophthalmic operation against diseases such as retina detachment, glaucoma, etc., a patient's eye is irradiated with laser energy, which is absorbed by a biological organism such as retina to develop thermal coagulation thereon for ophthalmological treatment. For this purpose, the laser coagulation system includes a laser spot projector for producing a laser beam from an argon or krypton laser, which is condensed to a laser beam spot of a predetermined diameter, directed toward a predetermined portion of the eyeball to be coagulated, and then focussed thereon as a laser spot for thermally coagulating the portion selected.
The laser coagulation system further comprises a slit image projector for forming a slit image on the eyeball to illuminate the background and to define the predetermined portion of the eyeball to be coagulated, and an observation equipment for observing the slit image and laser spot in the eyeball.
In such an arrangement, the laser spot from the laser spot projector must be changed in diameter depending upon how large the portion to be coagulated is. To adjust the diameter of the laser spot, the laser spot projector is conventionally provided with a magnification changing device of a type which has already been used in the field of the laser beam machining.
However, such a laser spot projector in the prior art has the drawbacks that the magnification changing device is complicated in structure, not compact and very hard to operate.